London Dispersion Helps Refine Steric A-Values: Dispersion Energy Donor Scales

Abstract

We suggest a scale of dispersion energy donors (DEDs) that allows for direct comparisons with steric effects. This scale is based on the classic A-values and allows groups to reorient to minimize strain, thereby providing an advantage over raw group polarizabilities. The A-value can no longer be considered purely a steric factor. Even for groups that do not participate in charge transfer or electrostatic interactions, the A-value includes Pauli repulsion (steric hindrance) and attractive London dispersion (LD) interactions. Although the common assumption is that, at the distances found in monosubstituted cyclohexanes, steric demands are the key factors influencing conformer preferences, we show in this computational study that there is a non-negligible LD part. We use this system to build a DED scale and a complementary steric scale. These scales are quantitatively comparable, as they are based on the same system, and allow for comparison of the two competing interactions in experimentally relevant settings. In addition, we show that LD interactions can be used to explain puzzling data regarding relative group sizes.

Dispersion stabilizes metal-metal bonds in the 1,8-bis(silylamido)naphthalene ligand environment

“…For example, the dispersive stabilization from bulky aryl and alkyl substituents has been found to be key in enabling the isolation of very reactive organometallic compounds and predicting reactivity. 11,[13][14][15][16][17][18][19] Similar studies have also been under- taken for carbene and phosphine ligands. [20][21][22][23] By comparison, few investigations have systematically and explicitly considered dispersive bond stabilization in complexes featuring bulky amide ligands, despite the prevalence of these ligands in coordination chemistry.…”

Silyl Groups Are Strong Dispersion Energy Donors

“…Considering the steric size of commonly utilized silyl groups, it is reasonable to hypothesize about the potential of these groups to serve as DEDs because they are far more polarizable. 43 with silyl groups directly attached in the 1,4-/1,6-position, and we demonstrated that an increase in size from TMS to extremely bulky tris(trimethylsilyl)silyl (TTMSS) leads to destabilizing internal strain on the COT backbone dominating the equilibrium between 1,4-and 1,6-COT. 44 The extended COT system under consideration here circumvents this problem.…”

“…This molecular balance consists of two distinct valence isomers (Scheme ) that can equilibrate via a double-bond valence bond isomerization. , For bulky tert -butyl substituents, experimental ,,, and computational , studies suggest the “folded” 1,6-isomer to be preferred in solution and in the gas phase. Considering the steric size of commonly utilized silyl groups, it is reasonable to hypothesize about the potential of these groups to serve as DEDs because they are far more polarizable . In a recent study, we have addressed the effective size of commonly used silyl groups by utilizing a disubstituted COT molecular balance with silyl groups directly attached in the 1,4-/1,6-position, and we demonstrated that an increase in size from TMS to extremely bulky tris­(trimethylsilyl)­silyl (TTMSS) leads to destabilizing internal strain on the COT backbone dominating the equilibrium between 1,4- and 1,6-COT .…”

Inhibition of Alkali Metal Reduction of 1‐Adamantanol by London Dispersion Effects

“…However, the combined total of multiple LD‐interactions in larger molecules can generate significant stabilization of the order of tens of kcal mol −1 . The importance of these effects has been highlighted in several studies, aided by more efficient computational methods [4a,b] …”